This application is based on patent application No. 11-39097 filed in Japan, the contents of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a process for producing hydroxyalkyl (meth)acrylates. Specifically, the present invention relates to an improved process which can commercially advantageously yield hydroxyalkyl (meth)acrylates from (meth)acrylic acid and alkylene oxides.
2. Description of the Prior Art
Hydroxyalkyl (meth)acrylates have been obtained by reacting (meth)acrylic acid with an alkylene oxide in the presence of a homogenous catalyst. Such homogenous catalysts include ferric chloride, iron hydroxide, and other iron compounds; chromium chloride and amine compounds; trialkyl amine, pyridine. However, such catalysts cannot be significantly separated from reaction mixtures for recycling, and are disadvantageous in cost efficiency.
These catalysts also serve to accelerate polymerization of the produced hydroxyalkyl (meth) acrylates. When the catalyst is transported into a distillation system for purification, it invites a distillation residue to polymerize thereby to become a gel, which will cause a blockage of equipment or other troubles.
As a possible solution to these problems, processes of using anion exchange resins as heterogenous catalysts have been proposed. For example, Japanese Examined Patent Publication No. 41-13019 discloses a process of using a catalyst comprising an ion exchange resin, most of whose ionic active groups are quaternary ammonium groups. Typical examples of the ion exchange resins used in this process are xe2x80x9cDIAION(copyright) SA10Axe2x80x9d (trade name: a styrene type anion exchange resin manufactured by Mitsubishi Chemical Corporation, Japan), and xe2x80x9cAmberlite IRA-400xe2x80x9d (trade name: a styrene type anion exchange resin manufactured by Rohm and Haas Co.).
Japanese Unexamined Patent Publication No.4-49265 discloses a process of using a catalyst comprising a strongly basic macroporous anion exchange resin having an acrylic backbone. Typical ion exchange resins used in the process include xe2x80x9cAmberlite IRA-958 (trade name: an anion exchange resin manufactured by Rohm and Haas Co.), and xe2x80x9cLewatit AP-247-Axe2x80x9d (trade name: an anion exchange resin manufactured by Bayer AG).
However, such known styrene type or acrylic type anion exchange resins have the following disadvantages.
The anion exchange resins having a trimethylammonium groups are known to be insufficient in heat resistance, and are believed to be used at temperatures of at highest about 50xc2x0 C. to 70xc2x0 C. In contrast, in the commercial production of hydroxyalkyl (meth)acrylates by the reaction of (meth)acrylic acid with an alkylene oxide, an optimum reaction temperature is 50xc2x0 C. or higher, and reaction temperatures as higher as possible are desirable to increase reaction rates to thereby improve reaction yields. The anion exchange resins which are insufficient in thermal stability cannot be effectively used as catalysts.
Specifically, the anion exchange resins under reaction conditions at high temperatures are liable to release the trimethylammonium group serving as a reactive group, which rapidly deteriorates the catalytic activity with the passage of reaction time. In addition, reaction products are contaminated by trimethylamine derived from the anion exchange resins, which causes, for example, deteriorated coloring tone of end products.
In order to improve the heat resistance of the anion exchange resins, an anion exchanger has been proposed in Japanese Unexamined Patent Publication No. 4-349941, which anion exchanger comprises a benzene ring bonded through a polymethylene chain with an ammonium group.
When the polyalkylene chain is an ethylene chain the resin is liable to be subjected to Hofmann degradation (an elimination reaction of trimethylamine). If a dimethyl group is introduced at the xcex1-position to yield 1,1-dimethylethylene chain to thereby inhibit the Hofmann degradation, the heat stability of the anion exchange group is deteriorated due to the steric hindrance between the both methyl groups at the xcex1-position [J. Appl. Polym. Sci., 8.1659(1964)].
The processes of using known ion exchange resins as catalysts, in which the chemical or thermal stability of the ion exchange resins is inferior, cannot commercially yield hydroxyalkyl (meth)acrylates from (meth)acrylic acid and alkylene oxides in good yields.
Accordingly, an object of the present invention is to solve the problems inherent to the conventional equivalents and to provide a process for economically efficiently producing hydroxyalkyl (meth)acrylates without disadvantages such as deterioration in properties of a distillation residue (gelation), by the use of a specific anion exchange resin having satisfactory thermal and chemical stability as a catalyst.
Specifically, in the invented process for producing hydroxyalkyl (meth)acrylates by the reaction of (meth)acrylic acid with an alkylene oxide, an anion exchange resin is used as a catalyst, which anion exchange resin containing a repeating unit represented by the following formula (1) as a component: 
wherein A is a straight chain alkylene group having 3 to 8 carbon atoms, each of R1, R2, and R3 is a hydrocarbon group or an alkanol group having 1 to 4 carbon atoms, which may be substituted with a hydroxyl group, Xxe2x88x92 is a counter ion coordinated with an ammonium group, where the substituent A with the ammonium group may be substituted at any position of a benzene ring, and part of hydrogen atoms bonded to the benzene ring may be substituted with an alkyl group or a halogen atom.
The present invention has a feature in that an anion exchange resin is used as a catalyst, which resin contains a repeating unit of the formula (1) as a component. As is apparent from the formula (1), the anion exchange resin for use in the invention can solve the problem of insufficient heat resistance in conventional anion exchange resins, by the introduction of a straight alkylene chain between an ion exchange group and a benzene ring. The anion exchange resin can therefore make (meth)acrylic acid to efficiently react with an alkylene oxide and can efficiently produce a hydroxyalkyl (meth)acrylate even at relatively high reaction temperatures.
The anion exchange resin for use in the invention having a repeating unit of the formula (1) is a polymer that is insoluble in a reaction system (a system in which reaction materials and products are present) of (meth) acrylic acid and an alkylene oxide. The substituent A in the formula (1) is a straight chain alkylene group having 3 to 8 carbon atoms.
The straight chain alkylene group A bonded to the ion exchange group is an essential element to improve the heat resistance of the ion exchange resin. If the number of carbons in the straight chain alkylene group A exceeds the above defined range, the constitutive unit of the formula (1) is to have an excessively large molecular weight, and an ion exchange capacity per unit mass is decreased to reduce the catalytic activity. Accordingly, the straight chain alkylene group A should have eight or less carbon atoms, preferably six or less carbon atoms. However, if the alkylene group A is an ethylene group or methylene group having two or less carbon atoms, the heat resistance is insufficient and a sustained satisfactory catalytic activity cannot be obtained. The straight chain alkylene group A must have three or more carbon atoms. Typically preferable examples of the alkylene group A are propylene group, butylene group, and pentylene group.
The alkylene group A having the ion exchange group may be substituted at any position of the benzene ring. The benzene ring in the formula (1) may be substituted with an alkyl group and/or a halogen atom. Such alkyl group include, but are not limited to, methyl group and ethyl group, and the halogen atom includes, for example, chlorine, bromine, and iodine atoms.
Each of groups R1, R2, and R3 in the group [NR1R2R3] serving as an anion exchange group is an alkyl group, or a hydroxyethyl group or another alkanol group having 1 to 4 carbon atoms, and may have a hydroxyl group as a substituent. These groups may be either different from one another, or identical to one another partially or totally. Specifically preferred group [NR1R2R3] is trimethylammonium group in which all of R1, R2, and R3 are methyl groups each having one carbon atom.
The ion Xxe2x88x92 in the formula (1) coordinates, as a counter ion, to the ammonium group serving as an ion exchange group. The counter ion includes, but is not limited to, Clxe2x88x92 and other halogen form ions, OHxe2x88x92 form ion, and an alcoholate (ROxe2x88x92) form ion. Preferred form of the counter ion is a salt form of the reaction material (meth)acrylic acid for use in the invention and/or the reaction product hydroxyalkyl (meth)acrylate.
The anion exchange resins each containing a repeating unit of the formula (1) as a component can be obtained synthetically by a variety of processes. Such production processes include, but are not limited to, a process described in Japanese Unexamined Patent Publication No. 4-349941.
Specifically, the anion exchange resin can be obtained by the copolymerization of a copolymerizable component having a constitutive unit of the formula (1) with a crosslinkable monomer having an unsaturated hydrocarbon, and when necessary with a third monomer having an unsaturated hydrocarbon. The crosslinkable monomer having an unsaturated hydrocarbon has two or more ethylenically unsaturated double bonds that are radical-polymerizable and is an essential component to obtained the anion exchange resin as a crosslinked polymer insoluble in the reaction system (the system in which reaction materials and products are present). Such monomers include, but are not limited to, divinylbenzene, polyvinylbenzene, alkyldivinylbenzene, dialkyldivinylbenzene, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, and polyethylene bis(meth)acrylamide. To ensure a sufficient physical strength in practice as a catalyst, the crosslinkable monomer(s) should preferably occupy 0.1% to 50% by mass, and more preferably 0.5% to 25% by mass in the overall monomers.
The unsaturated hydrocarbon-containing monomer for use as the third component includes, but is not limited to, styrene, an alkylstyrene, a polyalkylstyrene, a (meth)acrylic ester, (meth)acrylic acid, and acrylonitrile. The anion exchange resin can comprise the third component within the range not deteriorating the functions and properties required of the ion exchange resin. The content of the third component should be 50% by mass or less, and preferably 20% by mass or less in the overall polymerizable monomers.
The anion exchange resin for use as a catalyst in the invention can be molded into a wide variety of dimensions according to conventional technologies. The anion exchange resin should be preferably particle having a size of 100 xcexcm to 10 mm to exhibit the catalytic activities effectively, but it can be used in the form of lump, powder, fiber, membrane (film), or others if necessary. For example, the anion exchange resin can be used in the form of an ion exchange membrane or an ion exchange fiber.
A reaction for producing a hydroxyalkyl (meth)acrylate from (meth)acrylic acid and an alkylene oxide with the use of the catalyst can be performed with a stirring batch-system reactor, a fixed bed reactor, a fluidized bed reactor, or another reactor. The reaction system may be either a batch system or a continuous system.
Alkylene oxides for use in the synthetic reaction is an alkylene oxides each having preferably 2 to 6, more preferably an alkylene oxides each having 2 to 4 carbon atoms and the most preferably ethylene oxide and propylene oxide.
The alkylene oxide is used in an amount of equivalent mole or more, and preferably one to five times by mole that of the (meth)acrylicacid. The reaction temperature usually ranges from 50xc2x0 C. to 130xc2x0 C., and preferably from 50xc2x0 C. to 100xc2x0 C. If the reaction temperature is lower than 50xc2x0 C., the reaction rate is too low to obtain sufficient reaction efficiency. In contrast, if the reaction temperature exceeds 130xc2x0 C., the reaction materials and/or products are liable to be polymerized.
The synthetic reaction is generally performed in a liquid phase under pressure. The reaction pressure should be preferably such a pressure as to maintain the reaction mixture as a liquid phase. The atmosphere in the reaction is not particularly limited, but should be preferably a nitrogen atmosphere or another inert atmosphere.
A polymerization inhibitor is usually used in the synthetic reaction in order to inhibit the polymerization of the produced (meth)acrylate. The polymerization inhibitor is not limited, and can be freely selected from polymerization inhibitors for use in reactions of this type.
Typical examples of such polymerization inhibitors include hydroquinone, methylhydroquinone, tert-butylhydroquinone, 2,6-di-tert-butylhydroquinone, 2,5-di-tert-butylhydroquinone, 2,4-dimethyl-6-tert-butylphenol, hydroquinone monomethyl ether, and other phenolic compounds; N-isopropyl-Nxe2x80x2-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-Nxe2x80x2-phenyl-p-phenylenediamine, N-(1-methylheptyl)-Nxe2x80x2-phenyl-p-phenylenediamine, N,Nxe2x80x2-diphenyl-p-phenylenediamine, N,Nxe2x80x2-di-2-naphthyl-p-phenylenediamine, and other p-phenylenediamines; phenothiazine, thiodiphenylamine, and other amine compounds; copper dibutyl dithiocarbamate, copper diethyl dithiocarbamate, copper dimethyl dithiocarbamate, and other copper dialkyl dithiocarbamates; nitrosodiphenylamine, isoamyl nitrite, N-nitroso-cyclohexylhydroxylamine, N-nitroso-N-phenyl-N-hydroxylamine or its salt, and other nitroso compounds; 2,2,4,4-tetramethylazetidine-1-oxyl, 2,2-dimethyl-4,4xe2x80x2-dipropylazetidine-1-oxyl, 2,2,5,5-tetramethylpyrrolidine-1-oxyl, 2,2,5,5-tetramethyl-3-oxopyrrolidine-1-oxyl, 2,2,6,6-tetramethylpiperidine-1-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 6-aza-7,7-dimethyl-spiro(4,5)decane-6-oxyl, 2,2,6,6-tetramethyl-4-acetoxypiperidine-1-oxyl, 2,2,6,6-tetramethyl-4-benzoyloxypiperidine-1-oxyl, and other N-oxyl compounds.
The proportion of the polymerization inhibitor is usually about 0.001% to 1% by mass, and preferably about 0.01% to 0.5% by mass relative to the (meth)acrylic acid. The reaction can be performed in the presence of a solvent. Such solvents include, but are not limited to, benzene, toluene, xylene, hexane, heptane, petroleum ether and other solvents that are inert in the reaction.
According to the invention, hydroxyalkyl (meth)acrylates can be efficiently obtained in high yields by the coexistence of the anion exchange resin having a repeating unit of the formula (1) as a component in the reaction system.